.TH std::setw 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::setw \- std::setw

.SH Synopsis
   Defined in header <iomanip>
   /* unspecified */ setw( int n );

   When used in an expression out << std::setw(n) or in >> std::setw(n), sets the width
   parameter of the stream out or in to exactly n.

   Some operations reset the width to zero (see below), so std::setw may need to be
   repeatedly called to set the width for multiple operations.

.SH Parameters

   n - new value for width

.SH Return value

   An object of unspecified type such that

     * if out is an object of type std::basic_ostream<CharT, Traits>, the expression
       out << setw(n)
          * has type std::basic_ostream<CharT, Traits>&
          * has value out
          * behaves as if it called f(out, n)
     * if in is an object of type std::basic_istream<CharT, Traits>, the expression in
       >> setw(n)
          * has type std::basic_istream<CharT, Traits>&
          * has value in
          * behaves as if it called f(in, n)

   where the function f is defined as:

 void f(std::ios_base& str, int n)
 {
     // set width
     str.width(n);
 }

.SH Notes

   The width property of the stream will be reset to zero (meaning "unspecified") if
   any of the following functions are called:

     * Input

     * operator>>(basic_istream&, basic_string&)
     * operator>>(basic_istream&, char*)
     * Output

     * Overloads of basic_ostream::operator<<() that take arithmetic types or void
       pointers (at Stage 3 of num_put::put())
     * operator<<(basic_ostream&, char) and operator<<(basic_ostream&, char*)
     * operator<<(basic_ostream&, basic_string&)
     * std::put_money (inside money_put::put())
     * std::quoted (when used with an output stream)

   The exact effects this modifier has on the input and output vary between the
   individual I/O functions and are described at each operator<< and operator>>
   overload page individually.

.SH Example


// Run this code

 #include <iomanip>
 #include <iostream>
 #include <sstream>

 int main()
 {
     std::cout << "no setw: [" << 42 << "]\\n"
               << "setw(6): [" << std::setw(6) << 42 << "]\\n"
               << "no setw, several elements: [" << 89 << 12 << 34 << "]\\n"
               << "setw(6), several elements: [" << 89 << std::setw(6) << 12 << 34 << "]\\n";

     std::istringstream is("hello, world");
     char arr[10];

     is >> std::setw(6) >> arr;
     std::cout << "Input from \\"" << is.str() << "\\" with setw(6) gave \\""
               << arr << "\\"\\n";
 }

.SH Output:

 no setw: [42]
 setw\fB(6)\fP: [    42]
 no setw, several elements: [891234]
 setw\fB(6)\fP, several elements: [89    1234]
 Input from "hello, world" with setw\fB(6)\fP gave "hello"

   Defect reports

   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.

     DR    Applied to          Behavior as published          Correct behavior
   LWG 183 C++98      setw could only be used with streams of usable with any
                      type std::ostream or std::istream       character stream

.SH See also

   width      manages field width
              \fI(public member function of std::ios_base)\fP
   setfill    changes the fill character
              \fI(function template)\fP
   internal   sets the placement of fill characters
   left       \fI(function)\fP
   right
   showbase   controls whether prefix is used to indicate numeric base
   noshowbase \fI(function)\fP
